In some block based backup systems, file system objects (e.g., files, directories, etc.) are backed up by storing data blocks and metadata on backup media. Some block based backup systems achieve faster backup times compared to file based backup systems, particularly for high density file system applications where, for example, tens of millions of files are backed up. At a full backup, all data blocks associated with a file system or portion thereof being backed up are written to backup media and associated metadata is stored. During an incremental backup, only data blocks that have changed since a last backup are written to backup media and typically an incremental backup takes less time than a full backup.
During an incremental backup some current block based backup systems spend most of their time backing up metadata. It would be useful to develop techniques that would reduce the amount of time associated with backing up metadata during an incremental backup.